A pleated filter element comprises a sheet of filter material folded to form a plurality of parallel pleats or folds. The side edges of the sheet are brought together to provide a cylindrical configuration and the side edges are then joined together. In the conventional method of joining the side edges, one or both of the opposed side edges is coated with an adhesive and a sealed joint is then formed by application of heat to set the adhesive.
Difficulties have arisen in providing a positive seal between the side edges of the filter sheet, and in the past the seals have tended to be unreliable thereby permitting passage of solids through the filter element by edgewise flow through the side seam of the filter.
In the past a number of proposals have been made to increase the efficiency of the side seam seal. In U.S. Pat. No. 3,407,252 a heat sealable plastic tape is positioned between the side edges of the filter element and the tape bonds the ends through the application of heat and pressure.
In U.S. Pat. No. 3,867,294, the free side edges are provided with a reverse fold leaving a space in the form of a channel at the outer edge. A tape or ribbon of heat sealable adhesive is positioned within the channel, and when melted, provides a seam.
U.S. Pat. No. 4,184,966 discloses a seam sealing construction using a polypropylene channel-shaped strip to join the free side edges of the element, while U.S. Pat. No. 4,419,241 shows a flexible connecting strip inserted within the layers of the free side edges to provide a connection.
The seam sealing constructions for pleated filter elements, as used in the past, have been relatively expensive and in most cases the connected side edges did not have the same radial depth as the remaining pleats in the element. As a consequence, during service, movement or flutter of the connected side edges will occur because of pressure variations, particularly when the medium being filtered is cold and viscous, thereby resulting in tearing and failure of the filter element in this area.